Genetic variation in cholesterol ester transfer protein, serum CETP activity, and coronary artery disease risk in Asian Indian diabetic cohort

Lipid-Related Genetic Variants for Personalized Dietary Interventions: A Systematic Review

Dyslipidemias are known risk factors for chronic diseases. Precision nutrition interventions are designed according to characteristics, such as diet, phenotype, and genotype. This systematic review aims to define a panel of genetic variants associated with lipid abnormalities that could be later used in nutrigenetic intervention studies. A systematic review is conducted following the PRISMA-P. Studies published from January 2010 to December 2020 in English language and humans are included from PubMed and ScienceDirect databases. Articles that demonstrate a strong association between polymorphisms (single nucleotide variation) of genes involved in lipid metabolism and increased risk for dyslipidemia are included. A total of 3031 articles are screened, but only 51 articles fulfill the inclusion criteria. The genes included are FABP2, MTTP related to CM synthesis and secretion; LPL, LIPC involved in triglyceride hydrolysis; CETP, APOA1, LCAT, ABCA1, and APOA5 related to lipoprotein metabolism, and APOE, LDLR, SCARB1, APOC3 involved in lipid clearance. In this systematic review, genetic variants related to chylomicron synthesis, triglyceride hydrolysis, lipoprotein metabolism, and lipid clearance demonstrate a strong association with lipid abnormalities, which can be used to design precision nutrition interventions that may help to prevent and treat dyslipidemia effectively.

Gender Differences in the Association between Cholesteryl Esters Transfer Protein Polymorphism (rs708272) and Plasma Lipid Levels in Hyperlipidaemic Participants at Hospital Universiti Sains Malaysia

Background

Single nucleotide polymorphism (SNP) in the cholesteryl esters transfer protein (CETP) gene (rs708272) was reported to affect statin efficacy. This study investigated the association between CETP rs708272 and statin's lipid-lowering effects in hyperlipidaemic participants at Hospital Universiti Sains Malaysia, Kelantan.

Methods

A total of 229 hyperlipidaemic statin users (96.1% Malays) were recruited, and a single blood sample (3 mL) was obtained for DNA extraction. The genotypes were determined using PCR-RFLP method and validated by sequencing analysis.

Results

The minor allele frequency for rs708272 in all participants was 0.391, with no difference between females and males. At the baseline, the SNP was associated with different low-density lipoprotein (LDL-c) and triglyceride (TG) levels in females, but not males, when the GG and GA+AA genotypes were compared using a dominant genetic model. Regardless of the genotype, the total cholesterol and LDL-c levels decreased significantly (P < 0.001) in both genders after statin treatment, but the TG levels decreased exclusively in females with the GG genotypes. In both genders, high density lipoprotein levels were unaffected before and after the statin treatment.

Conclusion

To improve the management of hyperlipidaemia, future research should consider patient gender when assessing the CETP rs708272 impact on LDL-c and TG.

Autoimmune Reaction Associated With Long COVID Syndrome and Cardiovascular Disease: A Genetic Case Report

A 35-year-old woman with history of cardiovascular disease presented with shortness of breath, lightheadedness, fatigue, chest pain, and premature ventricular contractions 3 weeks after her second COVID-19 vaccine. Symptoms subsided following catheter ablation and ibuprofen except for chest pain and fatigue, which persisted following ablation and subsequent SARS-CoV-2 infection. The case suggests causal associations between COVID-19 vaccine/infection and recurrence of cardiovascular disease, including long-COVID-like symptoms. (Level of Difficulty: Advanced.).

Ethnic differences in ApoC-III concentration and the risk of cardiovascular disease: No evidence for the cardioprotective role of rare/loss of function APOC3 variants in non-Europeans

BACKGROUND

Hypertriglyceridemia is as an independent risk factor for cardiovascular disease (CVD). Apolipoprotein C-III (ApoC-III) is known to regulate triglyceride (TG) metabolism. However, the causal association between ApoC-III and CVD development is unclear. The objectives were to examine the impact of ApoC-III concentration on TG and lipoproteins and investigate the role of known rare loss-of-function APOC3 variants for modulating ApoC-III, TG concentrations and CVD risk in different ethnic groups.

METHODS

Plasma ApoC-III levels were measured in a multiethnic sample of 518 individuals comprising 271 Asian Indians (Sikhs), 87 Caucasians, 80 African Americans, and 80 Hispanics.

RESULTS

ApoC-III levels showed a robust association with TG in Asian Indians (r = 0.5, p = 1.1 × 10^-23), Caucasians (r = 0.4, p = 7.2 × 10^-4), and Hispanics (r = 0.9, p = 2.7x × 10^-28). African Americans had lowest ApoC-III and TG concentrations and highest (44%) prevalence of coronary artery disease (CAD). ApoC-III levels correlated with fasting blood glucose (r = 0.25, p = 6.1 × 10^-5) in Asian Indians and central adiposity in Hispanics (waist: r = 0.22, p = 0.05; waist-hip ratio: r = 0.24, p = 0.04). The carriers of rare variants IVS1-2G-A (rs373975305); A43T (rs147210663) and IVS3 + 1G-T (rs140621530) showed high TG but not low ApoC-III levels in Asian Indians and Caucasians.

CONCLUSION

These results highlight the challenges of generalizing antisense ApoC-III inhibition for treating atherosclerotic disease in dyslipidemia that may benefit only specific sub-populations. The observed ethnic differences in ApoC-III concentrations and CAD risk factors, emphasize in-depth genetic and metabolomics evaluations on diverse ancestries.

Mendelian Randomization of Dyslipidemia on Cognitive Impairment Among Older Americans

Background: Altered lipid metabolism may be a risk factor for dementia, and blood cholesterol level has a strong genetic component. We tested the hypothesis that dyslipidemia (either low levels of high-density lipoprotein cholesterol (HDL-C) or high total cholesterol) is associated with cognitive status and domains, and assessed causality using genetic predisposition to dyslipidemia as an instrumental variable. Methods: Using data from European and African genetic ancestry participants in the Health and Retirement Study, we selected observations at the first non-missing biomarker assessment (waves 2006-2012). Cognition domains were assessed using episodic memory, mental status, and vocabulary tests. Overall cognitive status was categorized in three levels (normal, cognitive impairment non-dementia, dementia). Based on 2018 clinical guidelines, we compared low HDL-C or high total cholesterol to normal levels. Polygenic scores for dyslipidemia were used as instrumental variables in a Mendelian randomization framework. Multivariable logistic regressions and Wald-type ratio estimators were used to examine associations. Results: Among European ancestry participants (n = 8,781), at risk HDL-C levels were associated with higher odds of cognitive impairment (OR = 1.20, 95% CI: 1.03, 1.40) and worse episodic memory, specifically. Using cumulative genetic risk for HDL-C levels as a valid instrumental variable, a significant causal estimate was observed between at risk low HDL-C levels and higher odds of dementia (OR = 2.15, 95% CI: 1.16, 3.99). No significant associations were observed between total cholesterol levels and cognitive status. No significant associations were observed in the African ancestry sample (n = 2,101). Conclusion: Our study demonstrates low blood HDL-C is a potential causal risk factor for impaired cognition during aging in non-Hispanic whites of European ancestry. Dyslipidemia can be modified by changing diets, health behaviors, and therapeutic strategies, which can improve cognitive aging. Studies on low density lipoprotein cholesterol, the timing of cholesterol effects on cognition, and larger studies in non-European ancestries are needed.

Association of CETP Gene Variants with Atherogenic Dyslipidemia Among Thai Patients Treated with Statin

Objective

Patients treated with statins for dyslipidemia may still have a residual risk of atherosclerotic cardiovascular disease (ASCVD). To determine whether genetic variants in the cholesteryl ester transport protein (CETP), rs3764261 (C>A), rs708272 (G>A), and rs12149545 (G>A) affect ASCVD risk, we studied the association of these variants with dyslipidemia in statin-treated patients.

Patients and Methods

We included 299 adult Thai patients treated with a statin (95 men and 204 women). Genotyping was performed by conducting a TaqMan real-time polymerase chain reaction-based analysis. We used logistic regression models adjusted for potential confounders of age, body mass index, blood pressure, insulin resistance, and statin dosage to analyze the association between CETP variants and atherogenic lipoprotein patterns.

Results

CETP polymorphisms of rs3764261 and rs708272, but not rs12149545, were significantly associated with high-density lipoprotein cholesterol (HDL-C), apoA-I, triglycerides, very low-density lipoprotein (VLDL)-C, and large LDL (LDL1-C) levels as well as mean LDL particle size (all p < 0.020). However, no significant difference was observed in total cholesterol, LDL-C, or apoB levels by CETP variants. Regardless of sex, the combination of rs3764261 (CC genotype) and rs708272 (GG or GA genotypes) showed a stronger association with atherogenic dyslipidemia, including features of decreased HDL-C, elevated triglycerides, and LDL subclass pattern B (odds ratio [OR] = 2.99, 95% confidence interval [CI]: 1.78–5.02) compared with the single variant rs3764261 (OR = 2.11, 95% CI: 1.27–3.50) or rs708272 (OR = 2.12, 95% CI: 1.29–3.49).

Conclusion

The polymorphisms of CETP rs3764261 (CC genotype) and rs708272 (GG and GA genotypes) may have a higher susceptibility to atherogenic dyslipidemia. Testing for CETP rs3764261 and rs708272 may serve as a surrogate marker for lipid management in statin-treated patients, which may help individualize treatment for reducing the residual risk of ASCVD.

Association of Serum Cholesterol Ester Transfer Protein Levels with Taq IB Polymorphism in Acute Coronary Syndrome

Information on the relationship between circulating cholesteryl ester transfer protein (CETP) levels and coronary heart disease (CHD) incidence (and also, therefore, acute coronary syndrome [ACS]) is conflicting. Many studies have been published concerning this relationship, most of which have incompatible results. In our study, we aimed to determine serum CETP levels in subject individuals with ACS and healthy control individuals, and the association of those levels with Taq IB polymorphism. The current study was conducted with 62 hospitalized patients who had been diagnosed with ACS and 26 controls. All subjects were selected from a previous study of which we are among the coauthors. Serum CETP levels were determined by quantitative enzyme-linked immunosorbent assay (ELISA). The mean serum CETP levels in all patients were significantly higher than those in controls. CETP TaqIB polymorphism affected serum CETP levels, with higher serum CETP for the GA genotype in both groups than in other genotypes. Although the AA genotype showed higher CETP levels than the GG genotype in patients with ACS, the GG showed higher CETP than the AA in healthy controls. Our results support an association between high serum CETP and ACS incidence. Our study helped address some of the controversies regarding the relationship of serum CETP mass to atherosclerosis, in addition to the association of ACS occurrence with circulating CETP levels.

Cholesteryl Ester Transfer Protein Genetic Variants Associated with Risk for Type 2 Diabetes and Diabetic Kidney Disease in Taiwanese Population

Cholesteryl ester transfer protein (CETP) plays an important role in lipid metabolism. Low levels of high-density lipoprotein cholesterol (HDL-C) increase the risk of type 2 diabetes (T2D). This study investigated CETP gene variants to assess the risk of T2D and specific complications of diabetic kidney disease (DKD) and diabetic retinopathy. Towards this, a total of 3023 Taiwanese individuals (1383 without T2D, 1640 with T2D) were enrolled in this study. T2D mice (+Lepr^db/+Lepr^db, db/db) were used to determine CETP expression in tissues. The A-alleles of rs3764261, rs4783961, and rs1800775 variants were found to be independently associated with 2.86, 1.71, and 0.91 mg/dL increase in HDL-C per allele, respectively. In addition, the A-allele of rs4783961 was significantly associated with a reduced T2D risk (odds ratio (OR), 0.82; 95% confidence interval (CI), 0.71–0.96)), and the A-allele of rs1800775 was significantly related to a lowered DKD risk (OR, 0.78; 95% CI, 0.64–0.96). CETP expression was significantly decreased in the T2D mice kidney compared to that in the control mice (T2D mice, 0.16 ± 0.01 vs. control mice, 0.21 ± 0.02; p = 0.02). These collective findings indicate that CETP variants in the promoter region may affect HDL-C levels. Taiwanese individuals possessing an allele associated with higher HDL-C levels had a lower risk of T2D and DKD.

Targeted sequencing of candidate genes of dyslipidemia in Punjabi Sikhs: Population-specific rare variants in GCKR promote ectopic fat deposition

Dyslipidemia is a well-established risk factor for cardiovascular diseases. Although, advances in genome-wide technologies have enabled the discovery of hundreds of genes associated with blood lipid phenotypes, most of the heritability remains unexplained. Here we performed targeted resequencing of 13 bona fide candidate genes of dyslipidemia to identify the underlying biological functions. We sequenced 940 Sikh subjects with extreme serum levels of hypertriglyceridemia (HTG) and 2,355 subjects were used for replication studies; all 3,295 participants were part of the Asian Indians Diabetic Heart Study. Gene-centric analysis revealed burden of variants for increasing HTG risk in GCKR (p = 2.1x10-5), LPL (p = 1.6x10-3) and MLXIPL (p = 1.6x10-2) genes. Of these, three missense and damaging variants within GCKR were further examined for functional consequences in vivo using a transgenic zebrafish model. All three mutations were South Asian population-specific and were largely absent in other multiethnic populations of Exome Aggregation Consortium. We built different transgenic models of human GCKR with and without mutations and analyzed the effects of dietary changes in vivo. Despite the short-term of feeding, profound phenotypic changes were apparent in hepatocyte histology and fat deposition associated with increased expression of GCKR in response to a high fat diet (HFD). Liver histology of the GCKRmut showed severe fatty metamorphosis which correlated with ~7 fold increase in the mRNA expression in the GCKRmut fish even in the absence of a high fat diet. These findings suggest that functionally disruptive GCKR variants not only increase the risk of HTG but may enhance ectopic lipid/fat storage defects in absence of obesity and HFD. To our knowledge, this is the first transgenic zebrafish model of a putative human disease gene built to accurately assess the influence of genetic changes and their phenotypic consequences in vivo.

Rare non-coding variants are associated with plasma lipid traits in a founder population

Founder populations are ideally suited for studies on the clinical effects of alleles that are rare in general populations but occur at higher frequencies in these isolated populations. Whole genome sequencing in 98 Hutterites, a founder population of European descent, and subsequent imputation revealed 660,238 single nucleotide polymorphisms that are rare (<1%) or absent in European populations, but occur at frequencies >1% in the Hutterites. We examined the effects of these rare in European variants on plasma lipid levels in 828 Hutterites and applied a Bayesian hierarchical framework to prioritize potentially causal variants based on functional annotations. We identified two novel non-coding rare variants associated with LDL cholesterol (rs17242388 in LDLR) and HDL cholesterol (rs189679427 between GOT2 and APOOP5), and replicated previous associations of a splice variant in APOC3 (rs138326449) with triglycerides and HDL-C. All three variants are at well-replicated loci in GWAS but are independent from and have larger effect sizes than the known common variation in these regions. Candidate eQTL analyses in in LCLs in the Hutterites suggest that these rare non-coding variants are likely to mediate their effects on lipid traits by regulating gene expression.

Association of Cholesterol Ester Transfer Protein Taq IB Polymorphism With Acute Coronary Syndrome in Egyptian National Patients

Background

The association between cholesterol ester transfer protein (CETP) Taq IB polymorphism and coronary artery disease (CAD) has been studied in different populations. Acute coronary syndrome (ACS) is a group of clinical symptoms within acute myocardial ischemia, including unstable angina (UA) and myocardial infarction (MI). Because there are no data reported in the literature concerning the cholesteryl ester transfer protein (CETP) Taq IB polymorphism in Egyptians, our study aimed to investigate the frequency of different CETP Taq IB genotypes in Egyptian patients with ACS and in healthy control individuals.

Methods

The current study was conducted with 70 hospitalized patients who had been diagnosed with ACS and 30 controls. We used real-time polymerase chain reaction (RT-PCR) to determine CETP Taq IB in individuals with different genotypes.

Results

The frequency of the GA genotype was significantly lower in UA patients, compared with the control group ( P  <.05).

Conclusions

The frequency of the CETP Taq IB genotypes and alleles in all groups was similar to that in other ethnic groups. Individuals with the Taq IB GA genotype may have a lower risk of UA.

Classical rather than genetic risk factors account for high cardiovascular disease prevalence in Lithuania: A cross-sectional population study

PURPOSE

Cardiovascular disease (CVD) mortality accounts for 54% of all deaths in Lithuania, making it the highest among all of the European Union countries. We evaluated the prevalence of several CVD risk factors, including lifestyle, blood biochemistry and genetic predisposition to determine the reasons behind significantly increased CVD prevalence in Lithuania.

MATERIALS AND METHODS

In total 435 volunteers of Lithuanian ethnicity and stable geographic settlement for 3 generations, had their anthropometric, biochemical and behavioural risk factors measured. A randomly selected sample of 166 volunteers had their 60 CVD risk alleles genotyped. The prevalence of risk alleles and cumulative CVD genetic risk score were compared with population of North-West European origin (CEU) using data from the phase 3 HapMap project.

RESULTS

CVD was present in 33.8% of study volunteers, 84% of participants consumed alcohol, 21% were current smokers and only 30% of participants engaged in higher levels of physical activity. Also, the average BMI (males 28.3±4.3kg/m², females 27.3±5.0kg/m²), total cholesterol (males 6.1±1.2mmol/L, females 6.2±1.0mmol/L) and LDL-cholesterol (males 4.1±1.1mmol/L, females 4.1±1.0mmol/L) were above the normal values. The cumulative genetic susceptibility to develop CVD in Lithuanians was only 1.4% higher than in CEU population.

CONCLUSIONS

High BMI and poor population plasma lipid profile are the major contributing factors to high CVD mortality and morbidity in Lithuania. Smoking, alcohol consumption and preliminary genetic predisposition results do not explain the difference in CVD mortality between the Lithuanian and wider European populations. CVD prevention programmes in Lithuania should primarily focus on weight loss and improving blood lipid control.

Common variants in the genes of triglyceride and HDL-C metabolism lack association with coronary artery disease in the Pakistani subjects

Background

Serum Triglyceride (TG) and High Density Lipoprotein (HDL-C) levels are modifiable coronary artery disease (CAD) risk factors. Polymorphisms in the genes regulating TG and HDL-C levels contribute to the development of CAD. The objective of the current study was to investigate the effect of four such single nucleotide polymorphism (SNPs) in the genes for Lipoprotein Lipase (LPL) (rs328, rs1801177), Apolipoprotein A5 (APOA5) (rs66279) and Cholesteryl ester transfer protein (CETP) (rs708272) on HDL-C and TG levels and to examine the association of these SNPs with CAD risk.

Methods

A total of 640 subjects (415 cases, 225 controls) were enrolled in the study. The SNPs were genotyped by KASPar allelic discrimination technique. Serum HDL-C and TG were determined by spectrophotometric methods.

Results

The population under study was in Hardy Weinberg equilibrium and minor allele of SNP rs1801177 was completely absent in the studied subjects. The SNPs were association with TG and HDL-C levels was checked through regression analysis. For rs328, the effect size of each risk allele on TG and HDL-C (mmol/l) was 0.16(0.08) and −0.11(0.05) respectively. Similarly, the effect size of rs662799 for TG and HDL-C was 0.12(0.06) and −0.13(0.0.3) and that of rs708272 was 0.08(0.04) and 0.1(0.03) respectively. The risk allele frequencies of the SNPs were higher in cases than controls, but the difference was not significant (p > 0.05) and SNPs were not associated with CAD risk (p > 0.05). The combined gene score of four SNPs significantly raised TG and lowered HDL-C but did not increase CAD risk.

Conclusion

The studied SNPs were associated with TG and HDL-C levels, but not with CAD in Pakistani population under study.

Electronic supplementary material

The online version of this article (doi:10.1186/s12944-017-0419-4) contains supplementary material, which is available to authorized users.

Taq1B Polymorphism of Cholesteryl Ester Transfer Protein (CETP) and Its Effects on the Serum Lipid Levels in Metabolic Syndrome Patients

The metabolic syndrome (MetS) is one of the most important risk factors for type 2 diabetes and cardiovascular disease. This syndrome is characterized by abdominal obesity, hypertension, insulin resistance, and dyslipidemia. The plasma origin of Cholesteryl ester transfer protein (CETP) is responsible for transferring cholesterol esters from high-density lipoprotein particles to apolipoprotein B containing lipoproteins compartment. We conducted this study to investigate the association between CETP gene Taq1B (rs708272) polymorphism in the metabolic syndrome among Iranian subjects. A sample size of 200 patients diagnosed with MetS together with 200 healthy donors as control were enrolled in this study. The investigation of polymorphism was performed by the use of polymerase chain reaction and restriction fragment length polymorphism analysis. To determine the relationship between polymorphism and lipid profile, we measured lipids and CETP concentration in metabolic syndrome and control subjects. Genotype distribution and allelic frequencies of polymorphism were determined and compared in both groups. Our findings showed that all clinical and biochemical characteristics in patients differed from the control group. The results showed that genotype and allele frequency of the Taq1B polymorphism was not significantly different between two groups. Instinctively, CETP was significantly higher in metabolic syndrome (1.64 ± 0.32 µg/ml) than in control (1.53 ± 0.34 µg/ml). A low level of CETP was found in blood of B2B2 typified genotype. In spite of Taq1B polymorphism on ester transfer protein concentration, no direct correlation was found between this polymorphism and metabolic syndrome.

Association of Cholesteryl Ester Transfer Protein and Endothelial Nitric Oxide Synthase Gene Polymorphisms With Coronary Artery Disease in the Multi-Ethnic Malaysian Population

Genetic variants of cholesteryl ester transfer protein (CETP) and endothelial nitric oxide synthase (eNOS) influence high-density lipoprotein cholesterol (HDL-C) metabolism and nitric oxide (NO) synthesis, respectively, and might increase the risk of coronary artery disease (CAD). This study is to investigate the relationship between genetic polymorphisms and the risk of CAD and to evaluate their potential interactions. A total of 237 patients with CAD and 101 controls were genotyped. The association of the polymorphism with the risk of CAD varied among the ethnic groups. Moreover, the concomitant presence of both CETP B1 and eNOS 4a alleles significantly increased the risk of CAD in the Malay group (OR = 33.8, P < .001) and the Indian group (OR = 10.9, P = .031) but not in the Chinese group. This study has identified a novel ethnic-specific gene–gene interaction and suggested that the combination of CETP B1 allele and eNOS 4a allele significantly increases the risk of CAD in Malays and Indians.

Genetic epidemiology of coronary artery disease: an Asian Indian perspective

Coronary artery disease (CAD) has emerged as a major cause of morbidity and mortality worldwide. Recent findings on the role of genetic factors in the aetiopathology of CAD have implicated novel genes and variants in addition to those involved in lipid and lipoprotein metabolism. However, our present knowledge is limited due to lack of clarity on their exact identity and the quantum of impact on disease susceptibility, and incident risk. It is a matter of great interest to understand the role of genetic factors in ethnic populations that have a strong underlying predisposition to CAD such as the South Asian populations, particularly among Asian Indians living in India and abroad. Although, a number of isolated studies do implicate certain gene polymorphisms towards enhanced disease susceptibility, the available data remains scanty and inconclusive as they have not been validated in large, prospective cohorts. The present review aims to consolidate the available literature on the genetics of CAD in Asian Indians and seeks to provide insights on the concerns that need to be addressed in future studies to generate information having clinical value.

Resequencing of the CETP gene in American whites and African blacks: Association of rare and common variants with HDL-cholesterol levels

BACKGROUND

Cholesteryl ester transfer protein (CETP) plays a crucial role in lipid metabolism. Associations of common CETP variants with variation in plasma lipid levels, and/or CETP mass/activity have been extensively studied and well-documented; however, the effects of uncommon/rare CETP variants on plasma lipid profile remain undefined. Hence, resequencing of the gene in extreme phenotypes and follow-up rare-variant association analyses are essential to fill this gap.

OBJECTIVE

To identify common and uncommon/rare variants in the CETP gene by resequencing the entire gene and test the effects of both common and uncommon/rare CETP variants on plasma lipid traits in two genetically distinct populations.

METHODS AND RESULTS

The entire CETP gene plus flanking regions were resequenced in 190 individuals comprising 95 non-Hispanic whites (NHWs) and 95 African blacks with extreme HDL-C levels. A total of 279 sequence variants were identified, of which 25 were novel. Selected variants were genotyped in the entire samples of 623 NHWs and 788 African blacks and 184 QC-passed variants were tested in relation to plasma lipid traits by using gene-based, single-site, haplotype and rare variant association analyses (SKAT-O). Two novel and independent associations of rs1968905 and rs289740 with HDL-C were identified in African blacks. Using SKAT-O analysis, we also identified rare variants with minor allele frequency <0.01 to be associated with HDL-C in both NHWs (P=0.024) and African blacks (P=0.009).

CONCLUSIONS

Our results point out that in addition to the common CETP variants, rare genetic variants in the CETP gene also contribute to the phenotypic variation of HDL-C in the general population.

Clinical Utility of a Coronary Heart Disease Risk Prediction Gene Score in UK Healthy Middle Aged Men and in the Pakistani Population

Background

Numerous risk prediction algorithms based on conventional risk factors for Coronary Heart Disease (CHD) are available but provide only modest discrimination. The inclusion of genetic information may improve clinical utility.

Methods

We tested the use of two gene scores (GS) in the prospective second Northwick Park Heart Study (NPHSII) of 2775 healthy UK men (284 cases), and Pakistani case-control studies from Islamabad/Rawalpindi (321 cases/228 controls) and Lahore (414 cases/219 controls). The 19-SNP GS included SNPs in loci identified by GWAS and candidate gene studies, while the 13-SNP GS only included SNPs in loci identified by the CARDIoGRAMplusC4D consortium.

Results

In NPHSII, the mean of both gene scores was higher in those who went on to develop CHD over 13.5 years of follow-up (19-SNP p=0.01, 13-SNP p=7x10^-3). In combination with the Framingham algorithm the GSs appeared to show improvement in discrimination (increase in area under the ROC curve, 19-SNP p=0.48, 13-SNP p=0.82) and risk classification (net reclassification improvement (NRI), 19-SNP p=0.28, 13-SNP p=0.42) compared to the Framingham algorithm alone, but these were not statistically significant. When considering only individuals who moved up a risk category with inclusion of the GS, the improvement in risk classification was statistically significant (19-SNP p=0.01, 13-SNP p=0.04). In the Pakistani samples, risk allele frequencies were significantly lower compared to NPHSII for 13/19 SNPs. In the Islamabad study, the mean gene score was higher in cases than controls only for the 13-SNP GS (2.24 v 2.34, p=0.04). There was no association with CHD and either score in the Lahore study.

Conclusion

The performance of both GSs showed potential clinical utility in European men but much less utility in subjects from Pakistan, suggesting that a different set of risk loci or SNPs may be required for risk prediction in the South Asian population.

Reassessing lipid metabolism and its potentialities in the prediction of cardiovascular risk

There are numerous particles, enzymes, and mechanisms in the lipid metabolism that are involved in the genesis of cardiovascular disease (CVD). Given its prevalence in populations and its impact on mortality, it is relevant to review the lipid metabolism as it may potentially provide subsidies to better prediction. This article reviews the importance of traditional cardiovascular risk factors and comments on the potential of novel lipid biomarkers involved in the physiopathology of CVD. The Framingham cohorts proved the role of traditional risk factors (physical inactivity, smoking, blood pressure, total cholesterol, LDL-C, HDL-C, plasma glucose) in the prediction of cardiovascular events. However, a significant number of individuals that suffer from a cardiovascular event has few or none of these factors. Such finding indicates the need for new biomarkers able to identify plaques that are more susceptible to rupture. Some of bloodstream biomarkers related to lipid metabolism are modified LDL particles, apolipoprotein AI (apo AI), apolipoprotein B, lipoprotein (a) [Lp (a)], cholesteryl ester transfer protein (CETP), subtypes of LDL and HDL particles, and lipoprotein-associated phospholipase A2 (Lp-PLA2). These factors participate in the atherosclerotic process, and are abnormal in individuals at high risk, or in those who suffered from a cardiovascular event. Lp (a) determination is already employed in clinical practice and should be included as a reference parameter for CVD monitoring. Furthermore, there are expectations for wider use of apo B, non-HDL cholesterol and total cholesterol / HDL-C determination to improve cardiovascular risk assessment.

Association of cholesteryl ester transfer protein (CETP) gene polymorphism, high density lipoprotein cholesterol and risk of coronary artery disease: a meta-analysis using a Mendelian randomization approach

BACKGROUND

Recent randomized controlled trials have challenged the concept that increased high density lipoprotein cholesterol (HDL-C) levels are associated with coronary artery disease (CAD) risk reduction. The causal role of HDL-C in the development of atherosclerosis remains unclear. To increase precision and to minimize residual confounding, we exploited the cholesteryl ester transfer protein (CETP)-TaqIB polymorphism as an instrument based on Mendelian randomization.

METHODS

The Mendelian randomization analysis was performed by two steps. First, we conducted a meta-analysis of 47 studies, including 23,928 cases and 27,068 controls, to quantify the relationship between the TaqIB polymorphism and the CAD risk. Next, the association between the TaqIB polymorphism and HDL-C was assessed among 5,929 Caucasians. We further employed Mendelian randomization to evaluate the causal effect of HDL-C on CAD based on the findings from the meta-analysis.

RESULTS

The overall comparison of the B2 allele with the B1 allele yielded a significant risk reduction of CAD (P < 0.0001; OR = 0.88; 95% CI: 0.84-0.92) with substantial between-study heterogeneity (I² = 55.2%; P(heterogeneity) <0.0001). The result was not materially changed after excluding the Hardy-Weinberg Equilibrium (HWE)-violation studies. Compared with B1B1 homozygotes, Caucasian carriers of the B2 allele had a 0.25 mmol/L increase in HDL-C level (95% CI: 0.20-0.31; P <0.0001; I² = 0; P(heterogeneity) =0.87). However, a 1 standard deviation (SD) elevation in HDL-C levels due to the TaqIB polymorphism, was marginal associated with CAD risk (OR =0.79; 95% CI: 0.54-1.03; P =0.08).

CONCLUSIONS

Taken together, our results lend support to the concept that increased HDL-C cannot be translated into a reduction in CAD risk.

Association of the variants in the PPARG gene and serum lipid levels: a meta-analysis of 74 studies

Considerable studies have been carried out to investigate the relationship between the polymorphisms of PPARG (Pro12Ala, C161T and C1431T) and serum lipid levels, but the results were inconclusive. Hence, we conducted a meta-analysis to clarify the association. MEDLINE, EMBASE and the Cochrane Library databases were searched systematically. The subgroup analysis was performed based on ethnicity. Seventy-four studies with 54,953 subjects were included in this meta-analysis. In Pro12Ala, the group with the ‘PP’ (C/C genotype) genotype group had lower levels of total cholesterol (TC) (mean difference, MD: −0.02, P < 0.00001; I² = 28%), low-density lipoprotein cholesterol (LDL-C) (MD: −0.02, P < 0.00001; I² = 30%) and higher levels of triglyceride (TG) (MD: 0.06, P < 0.00001; I² = 30%) than the combined ‘PA+AA’ (PA = C/G genotype, AA = G/G genotype) genotype group in Asian population, and the group with the ‘PP’ genotype had higher levels of TG (MD: 0.07, P < 0.02; I² = 67%) than the combined ‘PA+AA’ genotype group in non-Asian population. No statistically significant differences in the levels of TC, TG, high-density lipoprotein cholesterol, LDL-C were detected between different genotypes in C161T(Asian or non-Asian) and C1431T(Asian) polymorphisms. This meta-analysis was a renewed and confirmed study to assess the association between PPARG polymorphisms and serum lipid levels in Asian and non-Asian populations. There is a prominent association between Pro12Ala polymorphism and the levels of TC, LDL-C and TG in Asian population. No statistically significant differences in serum lipid levels were detected between different genotypes in C161T and C1431T polymorphisms.

Association of common genetic variants with lipid traits in the Indian population

Genome-wide association studies (GWAS) have been instrumental in identifying novel genetic variants associated with altered plasma lipid levels. However, these quantitative trait loci have not been tested in the Indian population, where there is a poorly understood and growing burden of cardiometabolic disorders. We present the association of six single nucleotide polymorphisms in 1671 sib pairs (3342 subjects) with four lipid traits: total cholesterol, triglycerides, high density lipoprotein cholesterol (HDL-C) and low density lipoprotein cholesterol (LDL-C). We also investigated the interaction effects of gender, location, fat intake and physical activity. Each copy of the risk allele of rs964184 at APOA1 was associated with 1.06 mmol/l increase in triglycerides (SE = 0.049; p = 0.006), rs3764261 at CETP with 1.02 mmol/l increase in both total cholesterol (SE = 0.042; p = 0.017) and HDL-C (SE = 0.041; p = 0.008), rs646776 at CELSR2-PSRC1-SORT1 with 0.96 mmol/l decrease in cholesterol (SE = 0.043; p = 0.0003) and 0.15 mmol/l decrease in LDL-C levels (SE = 0.043; p = 0.0003) and rs2954029 at TRIB1 with 1.02 mmol/l increase in HDL-C (SE = 0.039; p = 0.047). A combined risk score of APOA1 and CETP loci predicted an increase of 1.25 mmol/l in HDL-C level (SE = 0.312; p = 0.0007). Urban location and sex had strong interaction effects on the genetic association of most of the studied loci with lipid traits. To conclude, we validated four genetic variants (identified by GWAS in western populations) associated with lipid traits in the Indian population. The interaction effects found here may explain the sex-specific differences in lipid levels and their heritability. Urbanization appears to influence the nature of the association with GWAS lipid loci in this population. However, these findings will require replication in other Indian populations.

Genome-wide association study identifies variants in casein kinase II (CSNK2A2) to be associated with leukocyte telomere length in a Punjabi Sikh diabetic cohort

BACKGROUND

Telomere length is a heritable trait, and short telomere length has been associated with multiple chronic diseases. We investigated the relationship of relative leukocyte telomere length with cardiometabolic risk and performed the first genome-wide association study and meta-analysis to identify variants influencing relative telomere length in a population of Sikhs from South Asia.

METHODS AND RESULTS

Our results revealed a significant independent association of shorter relative telomere length with type 2 diabetes mellitus and heart disease. Our discovery genome-wide association study (n=1616) was followed by stage 1 replication of 25 top signals (P<10(-6)) in an additional Sikhs (n=2397). On combined discovery and stage 1 meta-analysis (n= 4013), we identified a novel relative telomere length locus at chromosome 16q21 represented by an intronic variant (rs74019828) in the CSNK2A2 gene (β=-0.38; P=4.5×10(-8)). We further tested 3 top variants by genotyping in UK cardiovascular disease (UKCVD) (whites n=2952) for stage 2. Next, we performed in silico replication of 139 top signals (P<10(-5)) in UK Twin, Nurses Heart Study, Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, and MD Anderson Cancer Controls (n=10 033) and joint meta-analysis (n=16 998). The observed signal in CSNK2A2 was confined to South Asians and could not be replicated in whites because of significant difference in allele frequencies (P<0.001). CSNK2A2 phosphorylates telomeric repeat binding factor 1 and plays an important role for regulation of telomere length homoeostasis.

CONCLUSIONS

By identification of a novel signal in telomere pathway genes, our study provides new molecular insight into the underlying mechanism that may regulate telomere length and its association with human aging and cardiometabolic pathophysiology.

An association study between genetic polymorphisms related to lipoprotein-associated phospholipase A(2) and coronary heart disease

Previous genome-wide association studies (GWAS) have revealed seven single nucleotide polymorphisms (SNPs) that affect lipoprotein-associated phospholipase A₂ (Lp-PLA₂) activity or levels in American and European individuals. A total of 290 coronary heart disease (CHD) patients, 198 non-CHD patients and 331 unrelated healthy volunteers were recruited for the present case-control study of Han Chinese. Four SNPs (rs964184 of ZNF259, rs7528419 of CELSR2 and rs7756935 and rs1805017 of PLA2G7) were shown to be significantly associated with CHD. The rs964184-G allele of the ZNF259 gene was identified as a risk factor of CHD in females (odds ratio (OR) =1.49, 95% confidence interval (CI) =1.00–2.22, P=0.05). The rs7528419-G allele of the CELSR2 gene was protective against CHD in males (OR=0.48, 95% CI=0.25–0.93, P=0.04). The other two alleles (rs7756935-C and rs1805017-A) of the PLA2G7 gene acted as protective factors against CHD in females (rs7756935-C: OR=0.59, 95% CI=0.35–1.00, P=0.05; rs1805017-A: OR=0.51, 95% CI=0.28–0.93, P=0.03). Moreover, rs1805017 of the PLA2G7 gene was associated with the severity of CHD only in females (r²=0.02, P=0.04). We identified four Lp-PLA₂-associated SNPs significantly associated with CHD in a Han Chinese population. Specifically, rs7528419 was protective factor against CHD in males, while the other two SNPs (rs7756935 and rs1805017 of the PLA2G7 gene) were protective factors against CHD in females and rs964184 of the ZNF259 gene was regarded as a risk factor for CHD in females.

Genetic determinants of cardiometabolic risk: a proposed model for phenotype association and interaction

This review provides a translational and unifying summary of metabolic syndrome genetics and highlights evidence that genetic studies are starting to unravel and untangle origins of the complex and challenging cluster of disease phenotypes. The associated genes effectively express in the brain, liver, kidney, arterial endothelium, adipocytes, myocytes, and β cells. Progression of syndrome traits has been associated with ectopic lipid accumulation in the arterial wall, visceral adipocytes, myocytes, and liver. Thus, it follows that the genetics of dyslipidemia, obesity, and nonalcoholic fatty liver disease are central in triggering progression of the syndrome to overt expression of disease traits and have become a key focus of interest for early detection and for designing prevention and treatments. To support the "birds' eye view" approach, we provide a road-map depicting commonality and interrelationships between the traits and their genetic and environmental determinants based on known risk factors, metabolic pathways, pharmacologic targets, treatment responses, gene networks, pleiotropy, and association with circadian rhythm. Although only a small portion of the known heritability is accounted for and there is insufficient support for clinical application of gene-based prediction models, there is direction and encouraging progress in a rapidly moving field that is beginning to show clinical relevance.

A replication study of GWAS-derived lipid genes in Asian Indians: the chromosomal region 11q23.3 harbors loci contributing to triglycerides

Recent genome-wide association scans (GWAS) and meta-analysis studies on European populations have identified many genes previously implicated in lipid regulation. Validation of these loci on different global populations is important in determining their clinical relevance, particularly for development of novel drug targets for treating and preventing diabetic dyslipidemia and coronary artery disease (CAD). In an attempt to replicate GWAS findings on a non-European sample, we examined the role of six of these loci (CELSR2-PSRC1-SORT1 rs599839; CDKN2A-2B rs1333049; BUD13-ZNF259 rs964184; ZNF259 rs12286037; CETP rs3764261; APOE-C1-C4-C2 rs4420638) in our Asian Indian cohort from the Sikh Diabetes Study (SDS) comprising 3,781 individuals (2,902 from Punjab and 879 from the US). Two of the six SNPs examined showed convincing replication in these populations of Asian Indian origin. Our study confirmed a strong association of CETP rs3764261 with high-density lipoprotein cholesterol (HDL-C) (p = 2.03×10⁻²⁶). Our results also showed significant associations of two GWAS SNPs (rs964184 and rs12286037) from BUD13-ZNF259 near the APOA5-A4-C3-A1 genes with triglyceride (TG) levels in this Asian Indian cohort (rs964184: p = 1.74×10⁻¹⁷; rs12286037: p = 1.58×10⁻²). We further explored 45 SNPs in a ∼195 kb region within the chromosomal region 11q23.3 (encompassing the BUD13-ZNF259, APOA5-A4-C3-A1, and SIK3 genes) in 8,530 Asian Indians from the London Life Sciences Population (LOLIPOP) (UK) and SDS cohorts. Five more SNPs revealed significant associations with TG in both cohorts individually as well as in a joint meta-analysis. However, the strongest signal for TG remained with BUD13-ZNF259 (rs964184: p = 1.06×10⁻³⁹). Future targeted deep sequencing and functional studies should enhance our understanding of the clinical relevance of these genes in dyslipidemia and hypertriglyceridemia (HTG) and, consequently, diabetes and CAD.